Etching bath and process for photoengraved plates



United States Patent 3,234,137 ETCHING BATH AND PROCESS FOR PHOTOENGRAVED lLATES Emile Lemaire, D 50 Quai St. Leonard, and Roger Lemaire, 24 Rue Morinval, both of Liege, Belgium No Drawing. Filed Oct. 3, 1962, Ser. No. 228,010 14 Claims. (Cl. 25279.4)

The present invention relates to improved baths and processes for etching metals, especially zinc and its alloys, intended for use in the production of photoengraved plates and other etched metal surfaces. This application is a continuation-in-part application of our applications Serial No. 28,019, filed May 10, 1960, and Serial No. 100,003, filed April 3, 1961, which in turn are continuation-in-part applications of our application Serial No. 815,790, filed May 29, 1959 all of which are now abandoned.

In the usual process for preparing photoengraved (line, halftone or combination) plates by a photomechanical process, an acid-resistant coating sensitive to light is applied to the surface of a metal plate. The sensitized surface is exposed to light through a negative image, so as to reproduce the corresponding image. The exposed surface is then developed to provide areas of acid resistant coating in the form of the corresponding image. The remaining portion of the metallic surface which is not protected by the remaining areas of the developed resist is subjected to an acid etching bath. The metallic plate is a zinc and/or magnesium base alloy. The etching solution conventionally used is an aqueous nitric acid solution containing various additives. This acid solution etches or corrodes those parts of the surface that are not protected by the image coating. Such an etching process results in the formation of depressions and hollows, the depth and size of which is a function of the line or halftone negative, of the concentration of acid in the solution, of the temperature, and of the other bath and process variables which affect the dissolution of metal in the acid solution.

For accurate reproductions, the acid should not deleteriously attack the protected surface of the metal plate. Since the acid will attack all unprotected metal, the problem arises that, as depressions in the surface are formed by the etching action, the acid also attacks laterally against the newly formed sides or shoulders of the depressions. Sufiicient lateral attack will cause the top surface to break down. The need still exists for aqueous acid baths which will etch the metal in the desired areas of the plate with minimal lateral attack.

It is one object of the present invention to provide improved baths and processes for the etching of photoengraving plates, including line, halftone and combination engravings.

It is another object of the present invention to provide novel compositions of matter, which, when diluted with hydrocarbon solvents and dissolved in aqueous nitric acid baths, provide such improved etching baths.

The additives which have heretofore been developed are primarily intended for use with plates of magnesium and their alloys, and while they have been used commercially for the etching of line, halftone and combination plates of zinc and its alloys, their results have been erratic and not completely satisfactory. The etching baths of the present invention, on the other hand, are especially useful with plates of zinc and its alloys and are useful under special conditions with plates of magnesium and its alloys.

Etching baths for photoengraved plates contain (1) nitric acid as the active etching agent; (2) organic compounds which function to form films on the lateral surfaces which are to be protected from attack by the etching The nitric acid basis) is present in the bath in amounts between about 30300 g./l.; and preferably between 50-150 g./l.

The nitric acid used in the process of the present invention is preferably the U.S.A. technical grade (42 B.) as distinguished from the usual photoengraving nitric .acid (40 B.) which contains various contaminating impurities, and alum. The use of photoengravers nitric acid in the process of the present invention leads to results which are far inferior to those obtained by the use of technical nitric acid which does not contain alum.

Film producing agents are present in the baths in amounts between 11 g./l. and 45 g./l., and preferably between 17 g./l. and 31 g./l. Two classes of film producing agents are present in etching baths. They are (a) oxygenated hydrocarbon compounds inamounts between 1 g./l. and 10 g./l. and, preferably, between 2 g./l. and 6 g./l.; and (0) liquid hydrocarbon solvents in amounts between 10 g./l. and 35 g./l. and, preferably, between 15 g./l. and 25 g./l.

Saturated carhoxylic acids, esters of carboxylic acids, sulfated oils and sulfated unsaturated acids have been previously disclosed as being useful as constituents of powderless etching baths. However, none have utilized sulfurized unsaturated acids, partially sulfated polymeric ricinoleic acid, sulfated olefinic acids nor any of them in combination with alkyl phenolic compounds condensed with ethylene oxide, thus combining anionic and nonionic wetting agents.

We have discovered that a superior etching bath is provided when the bath contains a non-ionic, partially sulfated, polymerized olefinic acid such as sulfated polymerized ricinoleic acid in the aqueous nitric acid etching bath, in combination with the liquid hydrocarbon and a very small amount of an alkylbenzenepolyethylene oxide adduct.

The partially sulfated polymerized ricinoleic acid used in the specific examples herein is commercially available as polymerized ricinoleic acid, but is to be carefully distinguished from the systematically named compoundpolymerized ricinoleic acid--which is not sulfated and is not readily commercially available.

Superior etching baths utilizing relatively small quantities of the partially sulfated polymerized ricinoleic acid require much less of such a sulfated acid than is required with sulfated ricinoleic acid. The results are superior both with respect to the etch factor, as well as with respect to the tone rendition in the halftone areas of a combination plate.

Thus, the etching baths of the present invention contain from about 1 g./l. to about 25 g./l. by weight of a sulfated polymerized ricinoleic acid, preferably from 1.5 to 6.0 g./l. and more preferably from about 1.5 g./l. to less than 4.0 g./l. by weight of such an acid in the total etching bath. These percentage additions are calculated on the basis of commercially available sulfated polymerized ricinoleic acid which contains from about 36 to about 38% by weight of water, and has a degree of sulfation equivalent to about 6% SO;, based on the total nonaqueous portion of the sulfated polymerized ricinoleic acid. As the water content of the sulfated material is reduced, the quantity of this sulfated acid needed may be reduced, and as the degree of sulfation is increased the amount of sulfated acid used may be reduced to some extent. However, the formulae and percentages herein: stated are based upon the commercially available material with its normal percentage of water content, and with its.

temperatures than room temperature and is also complete.

1y soluble in water in solutions more alkaline than pH 6.4. It normally is supplied as a very viscous liquid material, which is principally the sulfated polymeric condensation, product of ricinoleic acid apparently occurring principally as the guadrimer, trimer and dimer, but on addition of water and .heating and as actually used, it appears to be principally the partially sulfated dimer of ricinoleic acid.

The partially sulfated polymerized ricinoleic acid pre ferred for use in thepresent invention has an average molecular weight of about 750 to 810 and a sulfur con-;

tent of about 2.3% and may be prepared from castor oil by the following process:

, Castor oil is mixed with an excess of an aqueous solu tion of potassium hydroxide and boiled for 8 to 10 hours or until his fully saponified.

Afterstanding and cooling, dilute sulfuric acid is added with vigorous mixing While the mixture is held at about 80 C., and agitation is continued for about 2 hours. After standing several hours, the partially condensed ricinoleic acid separates and the sulfate-containing Water layor is separated.

Boiling water to the extent of about 50% by volume of the partially condensed ricinoleic acid is added and vigorously mixed for 1 or 2 hours to wash the oily product;

After standing for several hours, the oily product is decanted and to the oily product is added about by weight of 86% sulfuric acid. The acidified oily mixture is then heated for 14 to 16 hours at 80 to 90 C. so as to obtain a polymerized product which is a mixture of the dimer, trimer and quadrimer of the ester formed by reaction of the internal hydroxyl group with the terminal carboxylic groups and with some ofthe hydroxyl groups sulfated-by the sulfuric acid.

This product is then diluted with about 30% water and is neutralized by successive additions of a dilute sodium hydroxide-water solution, until it shows a pH of from about 6.5 to 6.7 in dilute aqueous solution. Thereafter, the partially sulfated, polymerized ricinoleic acid is separated fromthe most of the water to yield a final product which has from 36 tot38% water, about 2% ash, and about 70 to 72% of alcohol soluble material.

It is such a material which is herein referred to as the partially sulfated, polymerized ricinoleic acid.

The etching bath also includes a long chain (12 to 20 carbon atoms) fatty acid or its glyceride, or more preferably an unsaturated aliphatic acid or fat, such aslinoleic, palmitoleic, or oleic acid, preferably oleic acid and less preferably a glyceride of such unsaturated aliphatic acids. Alternatively, some or all of these fatty acids or their glycerides may be replaced by a sulfurized unsaturated aliphatic acid or its glyceride in which the double bond appears to have been eliminated and replaced. by a double. bond sulfur atom. A preferable quantity of-oleic, acid is from about 1.0 to 5.0 g./l. in the etching bath. When, sulfurized oleic is also used, it may also be presentin the bath from.l.0 to 5.0 g./l.

Such a sulfurizled oleic acid may be prepared by reacting oleic acid with sulfur. dichloride, one molecule of sulfur dichloride being used for each'molecule of oleic acid, or the oleicacid may be, directly reacted-with sulfur under prolonged heating. However, the sulfurized oleic acid, while useful, is not essential and may be omitted other olefinic acid employed in the etching bath.

In addition to the partially sulfated polymerized ricinoleic acid, the etching bath may contain a smaller amount 2 of sulfated oleic'acid, such as Prestabit oil V which is a partially sulfated oleic acidcontaining about 17% vby weight'of SO and inwhich from .40 to 50% of the oil is sulfatedi Thus, optionally the. etching bath I may contain up to about .3 g./l. of such a ,sulfated oleic acid.

In addition tothe sulfated polymerized ricinoleic acid and the olefinic acid, there is also provided a water-soluble,

non-ionici surface active agent comprising an alkyl phenol which has been condensed-with from 4 to 16 moles of ethylene oxide, of which the octylandnonyl phenols condensed with an average of about 8 or 9 moles of ethylene oxide are preferred. From about 0.02 g./l. to about 0.7

g./l., preferably from about 0.08 g./l. to 0.4 g./l. of the alkyl phenol-ethylene oxide adduct are used per liter of etching bath. 7

The polyethyenoxy ethers of alkylphenols areprcpared by condensing 4 to 16 moles (preferably averaging about 8 moles) of ethylene oxide with an alkylphenol, having; from 4 to 18 carbon atoms in the alkyl radical, such as diamylphenol or, most preferably, octylornonylphenol, and are sold commercially under the name Igepa Igepol (JO-610 is nonylphenol condensed with an average of 8 or 9 molecules of ethylene oxide.

The useful hydrocarbon solvents include varioustliquid T derivatives of petroleum and coal having a boiling range from about to 300 C. and preferably between and 225 0. They also include synthetic alkylaryl hydrocarbons suchias decylbenzene,; dodecylbenzene, tetrapropylbenzene, octodecylbenzene;dodecytoluene, 0ctodecy1- naphthalene, amylnaphthalene," of which we prefer to use dodecylbenzene or tetrapropylbenzene in amounts in the etching bath between 1 g./l. and 20 g./l. and, preferably,

between 3 g./l. and 8 g./l., together withsuflicient hydrocarbon from petroleum or coalto bringthe total hydro carbon liquid up to 10 g./l. to 35 g./l., preferably '15 g./l. to 25 g./l.

The petroleum solvent may be any of the relatively high boiling range petroleum-hydrocarbons, or such closely-cut,.highly aromatic solvents as-Solvesso 150 (boil- 1 ing range 187 to 21.1", C., 50% at 193) or Amscosolv G (boiling range 183 to 216 C., 50% at 199.5, 95%

at 211.5.), may be'substituted in whole or in part by other hydrocarbons such as diethylbenzene,or-dodecylbenzene or other hydrocarbons boiling up to about 260 C; or

somewhat higher.

The film producing agents are desirably in the aqueous bath in the form of a fine dispersion which is stable and, yet, which will break down at the new surfaces produced by the etching to deposit the necessary protective film.

The aqueous nitric: acid etching baths maybe made up by adding the various bath components'separately; For minimization of measurement errors and. for better control, it is preferred to premix the various organic compounds of the ,bath to form aliquid concentrate, which is then added to the bath.

The concentration of acid and the preferred concentration of. the other bath components is dependent-upon the type of etching machine as well as the type of photoengraved plates to be etched. The. concentrated additive mixture of organic compounds usedto makeup our preferred etching baths: consistsof between 30% and 85% 5 (percent by volume) of liquid hydrocarbon solvents, of which, preferably, at least 15% to 30% of the total addi tive is an alkylaryl compound; between 3% and 18% of at least one unsaturated acid; between 3% and 20% of polymerized partially sulfated ricinoleic acid, and between 0.1% and 2.0% of the polyethenoxy ether of an alkylphenol. The mixture, also, may contain between 1% and 5% of a lower alkyl ether of ethylene glycol or of propylene glycol, or an alkyl ether of an alkanol, preferably Butyl Cellosolve.

A highly concentrated additive liquid may be prepared, which may be suitably diluted by the user before adding it to the nitric acid etching bath, and is preferably compounded in the following proportions:

Partially sulfated polymerized ricinoleic acid ml 30 to 200 Oleic acid or olein ml 30 to 180 Sulfurized oleic acid ml to 180 flgepal (JO-610 ml 1 to 20 Butyl Cellosolve cc 0 to 50 Sulfated oleic acid ml 0 to 90 which is diluted with A to 4 times its volume with liquid -hydrocarbon such as Amsc'osolv G or dodecylbenzene prior to being added to the nitric acid etching bath.

For the purpose of giving those skilled in the art a better understanding of our invention the following il- 4 lustrative examples are given:

Example 1 A preferred nitric acid etching bath for the etching of zinc line engravings, zinc halftone plates and zinc combination (halftone and line) plates, comprises:

Water to make 138 liters.

Such an etching bath is used in the conventional manner, as in a Chemco powderless etching machine for the etching of zinc (or less desirably with magnesium plates) or in a Masters or other etching machine intended for similar use.

Preferably, the additive materials of Example 1 are mixed together, omitting the nitric acid and the water, and from 3 to 5 liters of such a mixture are added to the nitric acid and water and then diluted to make the 138 liters of etching bath required for loading a conventional type of etching machine.

Such a concentrated additive composition may comprise the ingredients in the following proportions which are given as percentages by volume:

Example 1-A Percent Partially sulfated ricinoleic acid 9.45

Oleic acid 6.55

Sulfurized oleic acid 4.62

Dodecylbenzene 18.60

Amscosolv G or Solvesso 150 58.30

Igepal 610 a 1.06

Butyl Cellosolve 1.42

An even more concentrated additive mixture may be prepared, in-which the Amsocosolv G or Solvesso 150 and/or the dedecylbenzene are omitted and are to be added by the user before or after the other ingredients have been'added to and dissolved in the acid bath.

6 Example 1-B Such a concentrated additive composition comprises, in its preferred form:

This is first diluted for use with about 3 times its volume of petroleum hydrocarbons and dodecylbenzene or other aromatic hydrocarbon, after which preferably 4.0 liters, or from 3 to 5 liters are added to 138 liters of nitric acid etching bath containing about 8.5% nitric acid.

The aqueous nitric acid etching baths may be prepared by dissolving the mixtures of organic compounds noted in the Examples 1-A, lB, 2-A, 2-B, and 5 in aqueous solutions containing between 3% and 30% by weight of nitric acid, most preferably in an aqueous solution of technical 42 B. nitric acid, to produce a bath containing about 12% technical acid or 8.45% of nitric acid.

The partially-sulfatedpolymerized ricinoleic acid may be substituted in part by sulfated oleic acid or a salt thereof and for thispurpose we prefer to use the sodium salt of sulfated oleic-acid containing about 17% by weight of -SO and being approximately 42.5% fully sulfated oleic acid, commercially available as Prestabit oil V. This is water-soluble clear liquid which has a pH from abolut 5.5 to 7.5 in a 10% water solution.

Example 2 An excellent etching bath according to the present invention is prepared in accordance with the following formula:

For ease in preparing the bath, the additive may be compounded on the basis of the following formula:

Vol. percent Partially sulfated polymerized ricinoleic acid 7.4 Oleic acid 9.3 Prestabit oil V 0.4 Amscosolv G 61.3 Dodecylbenzene 19.6 Igepal CO-610 0.5 Butyl Cellosolve (optional) 1.5

This additive is diluted with from 27 to 46 volumes, preferably about 35 volumes, of aqueous solution containing from 3 to 30% of nitric acid, preferably from 6 to 10%, and most preferably about 8.5% nitric acid.

Example 2-B In case it is desired to ship only the minor ingredients of the additive composition so that the user may add his own hydrocarbon liquidto the etching bath, the concentrated additive of this example comprises:

Vol. percent Partially sulfated polymerized ricinoleic acid 39.1 Oleicacid 48.5 Prestabit oil V 2.0 Igepal CO-610 2.6 Butyl Cellosolve 7.8

7 Example 3 A substantial proportion of the unsaturated fatty acid may be replaced with a quantity of sulfurized unsaturated acid, such as sulfurized oleic acid, and another illustrative example of such an additive is as follows:

Vol. percent Partially sulfated polymerized ricinoleic acid 9.45 Oleic acid 6.55- Sulfurized oleic acid 4.62 'Igepal CO-610 1.06 Amscosolv G 58.3

Dodecylbe'nzene 18.6 Butyl Cellosolve 142 From 3 to 5 liters of this additive are added to an aqueous solution of nitric acid to form 138 liters of an etching. bath having about 8.5% nitric acid.

Example 4 Another etching bath according to the present invention is prepared as follows:

Octylphenol condensed with'an average of 8 moles of ethylene oxide 0.5 Butyl propylene glycol .1- 1 Petroleum hydrocarbon liquid 12 Dodecylbenzlene 5 Dehydrated ricinoleic acid 5 Nitricfacid 42 Be. 100

Water to make 1 liter. 7

In general quantities of the sulfated polymerized ricinoleic acid and other sulfated materials greater than 1 about 0.3% in the etching bath are not as eifective as etching baths containing smaller amounts, although the optimum quantities of the sulfated materials will depend upon the degree of sulf ation, and upon the water-content of thesulfated material.

Also in general, the specific hydrocarbon liquids employed are not critical, but they are preferably relatively non-volatile so as to reduceloss by evaporation with the attendant fire hazard, while higher'boiling hydrocarbons tend to be too-viscous;

Example 5 Another etching bath additive producing excellent results in the etching of combination plates of zinc in either a Chemco or a Master etching machine, such as are commonly used in the powderless etching ,of such plates, comprises:

Vol. percent Partially sulfiated polymerized ricinoleic acid 9.69 Oleic acid 9.00 Igepal CO-610 0.61 Butyl Cellosolve 1.45 A-mscosolv G 60.10 Dodecylbenzene 19.15

From 3 to 5 liters of this additive (preferably about 4 liters) are dissolved in aqueous nitric acid to provide 138 liters of a solution containing about 8.5% by weight of nitric acid.

Example 6 Much larger quantities of the partially sulfated polymw erized ricinoleic acid may be'used by suitable adjustment of the quantity of oleic acid and petroleum solvent, and one such formula is as follows:

Nitric acid 42 B'. sufficient to'make' liters.

The invention in its broader aspects is not limited to the specific. steps, processes and compositions shown and described but departures may be .made therefrom within the scope of the, accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is;

1. A method for powderless etching of plates of zinc, magnesium andtheir alloys which comprises impinging against the surface. of the plate, portionsof which are protected by a resist layer, an etching bath comprising, per liter of etching bath," from'30 to 300 grams of nitric acid,

from 1 to 25 grams of a partially sulfated polymerized.

ricinoleic acid, having a molecular weight of from about 750 to about 810 and'a sulfur content "of about 2.3% from 10 to 35 grams of a liquid hydrocarbomboiling within the range of from about C. to about 300 C., from 1 to 5 grams of an unsaturated aliphatic acid selectedirom the group consistingof oleic acid, linoleic acid and'pal'mitoleicacid and from 0.02 to 0.7 gram of a water-soluble, non-ionic surface active agentwhichis a polyethyleneoxy ether of'a'n alkyl phenol having from 4 to 18 carbon atoms in the alkyl; group, the ratio of eth ylene oxide to. alkyl phenol in the; said ether being from 4 to 16 moles of ethylene oxide per mole of alkyl phenol.

2. A method as recited in claim 1 in which the nitric acid is derived from technical gnade vnitric acid., 7

3. A method asrecited in claim 1 in which the etching bath also includes froml to. 5 grams per. liter of sulfurized oleic acid.

4. A methodas recited in'claim 1 in which the etching bath also includes up to 0.3 gram per liter of sulfated.

oleic acid. 5. An etching bath for powerless etching of'pltates of zinc, magnesium, and their alloys comprising, per liter of etching bath, from 30to 300 grams of nitric acid, from 1 1 to 25 grams of a partially sulfated polymerized .ricinoleic acid, having a molecular weight of from about 750 toabout =810 and a sulfur content of about 2.3%, from 10 to a 35 grams of a liquid hydrocarbon, boiling within the range of from about 100 C. to about 300.C., fro'ml to 5 grams of an unsaturated aliphatic, acid selected from the group-consisting of oleic acid, linoleicacid and palrnitoleic tacidand from 0.02 to 0.7 gram of a watersoluble, non-ionic surface-active agent which is a polyethyleneoxy' ether of an alkyl phenol having from 4 to 18 carbonatoms in the alkyl group, the ratio of ethylene oxide to alkyl phenol in the ether being from 4 to 16 moles of ethylene oxide per mole of alkyl phenoLi 6. An additive composition to be diluted with liquid hydrocarbon boiling Within the range. of from about 100 C. to 300 C. and added to an aqueous solution of nitric acid for the powderless etching of plates, which comprises the following ingredients in the following proportions: about 30 to 200 ml. of partially .sulfated polymerized ricinoleic acid, having a molecularweight of from about 750 to about. 810 and a sulfurvcontent of about 2.3%,

about 1 to 20 ml. of a water-soluble, non-ionic, surfaceactive polyethyleneoxy ether of an alkyl phenol having from 4 to 18 carbon atoms in the alkyl group, the ratio of ethylenev oxide-"to alkyl phenol in the ether being from 4 to 16 moles of ethylene. oxide per mole of alkyl phenol a liquidhydroearbon boiling within therange of from about100 C. to 300 C.

v10. An additive composition to be added to an aqueous bath of nitric acid for the powderless etching of plates comprising from about 3% to 20% by volume of partially sulfated polymerized ricinoleic acid having a molecular weight of from about 750 to about 810 and a sulfur content of about 2.3%, from about 0.1% to about 2% by volume of a water-soluble, non-ionic surface-active agent which is a polyethylene oxyether of an alkyl phenol having from 4 to 18 carbon atoms in the alkyl group, the ratio of ethylene oxide to alkyl phenol being from 4 to 16 moles of ethylene oxide per mole of alkyl phenol, from about 30% to 85% by volume of liquid hydrocarbon boiling within the range of from about 100 C. to about 300 C. and from about 3% to 18% by volume of at least one unsaturated aliphatic acid selected from the group consisting of oleic acid, linoleic acid and. palmitoleic acid.

11. An additive composition to be diluted with liquid hydrocarbon having a boiling point within the range from 100 C. to about 300 C. and added to an aqueous solution of nitric acid for the powderless etching of plates, which comprises water-soluble and water-insoluble components, said water-soluble component comprising sulfateradical containing, polymerized ricinoleic acid, having a molecular weight of from about 750 to about 810 and a sulfur content of about 2.3% and a smaller amount of a water-soluble, non-ionic, surface-active polyethyleneoxy ether of an alkyl phenol having from 4 to 18 carbon atoms in the alkyl group, the ratio of ethylene oxide to alkyl phenol in the ether being from 4 to 16 moles of ethylene oxide per mole of alkyl phenol, and said water-insoluble component comprising at least one unsaturated aliphatic acid selected from the group consisting of oleic acid, linoleic and palmitoleic acid in an amount much smaller than the amount of liquid hydrocarbon with which the additive is to be used.

12. An etching bath for the etching of plates for use in photoengraving processes consisting essentially of, per liter of etching bath:

(a) nitric acid, from about 50 to about 150 grams;

(b) a partially sulfated, polymerized ricinoleic acid having a molecular weight of from about 750 to about 810 and a sulfur content of about 2.3%, from about 1.5 to about 4 grams;

10 (c) an unsatunated fatty acid selected from the group consisting of oleic acid, linoleic acid and palmitoleic acid, from about 1 to about 5 grams; (d) a polyethyleneoxy ether of an alkyl phenol having 5 from 4 to 18 carbon atoms in the alkyl group, the ratio of ethylene oxide to |alkyl phenol in the ether being from 4 to 16 moles of ethylene oxide per mole of alkyl phenol;

(e) liquid hydrocarbon having a boiling point within the range from about 150 to 225 C., from about 15 grams to 25 grams, of which from about 3 grams to about 8 grams consists of a hydrocarbon selected from the group consisting of dodecylbenzene and tetrapropylbenzene;

(f) a glycol derivative selected from the group consisting of ethylene glycol monobutyl ether, propylene glycol, diethylethylene glycol and dibutylpropylene glycol; and

(g) water.

13. An etching bath as recited in claim 12 wherein the unsaturated fatty acid is oleic acid.

14. An etching bath as recited in claim 13 also including a sulfated oleic acid.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Emulsions and Detergents, Union Carbide and Carbon Corp., Ninth Ed., pages 75 and 76 (1955).

Zimmerman et al.: Handbook of Material Trade 40 Names, 1935 ed., page 462.

JULIUS GREENWALD, Primary Examiner.

ALBERT T. MEYERS, Examiner. 

1. A METHOD FOR POSDERLESS ETCHING OF PLATES OF ZINC, MAGNESIUM AND THEIR ALLOYS WHICH COMPRISES IMPINGING AGAINST THE SURFACE OF THE PLATE, PORTIONS OF WHICH ARE PROTECTED BY A RESIST LAYER, AN ETCHING BATH COMPRISING, PER LITER OF ETCHING BATH, FROM 30 TO 300 GRAMS OF NITRIC ACIE, FROM 1 TO 25 GRAMS OF A PARTIALLY SULFATED POLYMERIZED RICINOLEIC ACID, HAVING A MOLECULAR WEIGHT OF FROM ABOUT 750 TO ABOUT 810 AND A SULFUR CONTENT AF ABOUT 2.3% FROM 10 TO 35 GRAMS OF A LIQUID HYDROCARBON, BOILING WITHIN THE RANGE OF FROM ABOUT 100*C. TO ABOUT 300*C., FROM 1 TO 5 GRAMS OF AN UNSATURATED ALIPHATIC ACID SELECTED FROM THE GROUP CONSISTING OF OLEIC ACID, LINOLEIC ACID AND PALMITOLEIC ACID AND FROM 0.02 TO 0.7 GRAM OF A WATER-SOLUBLE, NON-IONIC SURFACE ACTIVE AGENT WHICH IS A POLYETHYLENEOXY ETRHER OF AN ALKYL PHENOL HAVING FROM 4 TO 18 CARBON ATOMS IN THE ALKYL GROUP, THE RATIO OF ETHYLENE OXIDE TO ALKYL PHENOL IN THE SAID ETHER BEING FROM 4 TO 16 MOLES OF ETHYLENE OXIDE PER MOLE OF ALKYL PHENOL. 